Lancets are used to lance an appropriate body part to generate a wound and collect blood from a body part (usually from the finger or the earlobe) for diagnostic purposes. Specially trained personnel are required if this is carried out manually. The puncture is nevertheless associated with considerable pain.
Blood collection systems have been used for a long time which are composed of a lancing device and associated lancets that are specially adapted to the respective device. A lancet drive which mechanically drives a lancet into the skin is located in a housing of the lancing device. A spring is usually used as the driving element for the lancing movement.
However, it is frequently necessary for a patient to be subjected several times daily to an examination in order to regularly monitor certain analytical blood values. This applies particularly to diabetics who must frequently check their blood sugar level in order to maintain it as constant as possible within certain required limits, which is accomplished by taking insulin injections as needed based upon the blood sugar level that is measured. Blood sugar levels may vary greatly depending on food intake, physical activity, etc.
Consequently, a prerequisite for this intensive therapy is that the blood collection cause as little pain as possible. Numerous different blood collection systems which comprise mechanical drive units for a lancet or needle have been developed with the aim of minimizing pain. Nowadays, such drive units are so highly developed that the lancing process can be carried out reproducibly in a relatively painless manner. However, before the blood collection system can be operated, a drive element, which is frequently a spring of the drive unit, must be transferred into a tensioned position. When the lancing process is subsequently triggered, the drive element is again transferred into a relaxed position. The energy which is released by the drive element in this process is used to drive the lancet in the lancing direction.
However, a disadvantage of the prior art is that the tensioning process of a blood collection system often requires significant force and/or complex handling steps by the user in the case of a blood collection system having a mechanical drive unit. For example, in the document DE 10223558.9, the tensioning of a blood collection system is described in which a spring is tensioned in the drive unit by turning a knob on the housing. This requires the patient to use both hands to operate the device.
Such handling steps are often perceived to be difficult by older persons or people with limited motor skills. Hence, in addition to a puncture that is as pain-free as possible, easy operation of the blood collection system is desirable, especially in the intensive therapy that is often required for elderly people.
Blood collection systems with an automatic drive have been described in the prior art which should enable simple and comfortable handling, especially for persons with motoric disabilities. The user is thus spared to the extent possible in some cases the complicated process of tensioning the lancets and the subsequent triggering of the lancing process. The patient can activate an electrical drive mechanism by pressing a button without additional handling steps or exerting force. The documents WO 02/100461, WO 02/100460 as well as WO 02/00101 and WO 02/100251 each disclose blood collection systems in which an electrical drive unit moves the lancet in the drive direction and executes a lancing process. For example, electromagnetic drive elements are mentioned in the document WO 02/100251. The transfer of force from the drive units to the lancet body is controlled by control units in such a manner that a defined lancing movement can take place.
An automatic blood collection system comprising a plurality of lancets is also disclosed in U.S. Pat. No. 6,530,892. The drive unit is realized by a magnet analogously to the above-mentioned prior art.
The systems described each utilize electrical drive units. A rapid transfer of force to the lancet, which converts the electrical energy into a movement of the lancet body, requires additional components. In order to achieve a high drive speed using electrical drive units, capacitors are typically integrated into an electrical drive unit and provide the energy required for lancing by a rapid discharge. This arrangement attempts to transfer the energy rapidly and directly from the electrical drive unit onto the lancet. Although electrical drive units are particularly suitable for use as a long-term store in lancing aids due to their high storage density of greater than 100 joules per gram, it has, however, been found that the rate at which energy can be removed from electrical drive units is usually limited to about 10 joule/sec due to a given internal resistance. Moreover, the efficiency of the system deteriorates as the rate of removal increases. Furthermore, additional measures are necessary to control a defined motion sequence of the lancet body in which the lancet pierces a body part of a patient in a vibration-free manner and the subsequent retraction of the lancet into the blood collection system is as desired.
Consequently, a disadvantage of the described prior art is that complicated control mechanisms which control a defined motion sequence of the lancet body during the lancing process are required in addition to the electrical drive units. Because of the presence of the electrical drive unit, it is not possible to integrate the already well-proven mechanical drive mechanisms into the system. Hence, one is not able to utilize the advantages of mechanical drive units which have been significantly improved in recent years and now enable a relatively painless lancing due to precisely defined sequences of motion.
Hence, complicated additional measures have to be implemented for electrical drives in order to control the lancing process in a manner comparable to that of mechanical drive units, and these measures still often prove inadequate in comparison to mechanical drive units. Furthermore, the additional components that are necessary for electrical drives, such as capacitors and control units, complicate the design of a lancing aid and thereby increase its manufacturing costs. Moreover, in addition to inadequate control of the motion sequence, the transfer of force from the drive unit to the lancet body is often delayed, resulting in a retarded motion sequence of the lancet body. This in turn increases pain from lancing. Hence, a comparison of electrical drive units with mechanical drive units shows that, although electrical drive units provide a higher storage density that is available to the system, the rate of removal and thus the force transfer of the drive unit onto the lancet body is often inadequate.
Thus, blood collection systems having an electrical drive unit present difficulties in satisfying the requirements of a relatively painless puncture.
In contrast, the use of a mechanical drive unit is defined by a high removal rate as is urgently required for a lancing movement of a lancet. Conventional springs provide a high removal rate of a few thousand joules per second at an almost ideal efficiency. However, mechanical drive units which are often in the form of a spring, prove inefficient as energy stores because they require large volumes for a high storage density. For example, compared to electrical drive units, a spring used in a typical mechanical drive unit has a low storage density of only about 150 mJ per gram. Consequently, in view of the compact designs of blood collection systems which are required in modern analytics, it is not possible to achieve a high storage density with a mechanical drive.
Furthermore, the use of mechanical drive units often necessitates a complicated handling by the user that requires much force which, as already discussed above, is regarded as disadvantageous.
Hence, it has become increasingly apparent in recent years that there is a great interest in a blood collection system which simultaneously fulfills the difficult and partly contrary requirements of minimal pain sensation, simple operation, compact, slimmest possible design, and as simple and economical a construction as is possible.